Pressure sensors (or transducers) are used in various applications to measure the pressure of gases and liquids. Pressure sensor designs must take into consideration the possibility that the element being measured will undergo a phase change in response to a corresponding temperature change (e.g. a fluid being measured may freeze). In the case of a fluid freezing, ice may form in and around the pressure sensor, as well as in the associated plumbing interface. The volumetric expansion of these ice formations may cause large forces to be exerted both within internal portions of the sensor as well as on external portions of the sensor exposed to the fluid. These forces can be hundreds to thousands of times the rated pressure of the sensor, and thus, can lead to significant damage to the sensor.
In one particular application, urea injection systems use a mixture of urea and liquid water injected into a catalytic reactor to reduce mono-nitrogen oxide (NOx) levels in diesel and other internal combustion engine exhaust. In order to accomplish this, a storage tank of urea must be onboard, in addition to a pump, pressure sensors, plumbing and the like. Pressure sensors are required for measuring the urea injection pressure and to aid in precisely controlling the mixture of urea and exhaust gases. If urea is allowed to freeze (typically at −11 degrees C.) in the plumbing of the system, it can create significant pressures (e.g. in excess of 100,000 psi) depending on the specific system geometry, and may destroy sensitive system components including the pressure sensors themselves. To combat the freezing of urea, early systems implemented a pump down sequence for purging a system's urea lines. However, newer systems are required to be rated for multiple freeze cycles in case the purge cycle does not occur, such as in the case of a dead battery.
Alternative systems and methods for protecting pressure sensors from pressure overload and mechanical damage due to freezing conditions are desired.